The present invention relates to a plasma arc torch having an improved water injection nozzle assembly.
Plasma arc torches are commonly used for the working of metals, including cutting, welding, surface treatment, melting, and annealing. Such torches include an electrode which supports an arc which extends from the electrode to the workpiece in the transferred arc mode of operation. It is also conventional to surround the arc with a swirling vortex of gas which forms the plasma arc, and in some torch designs the gas and arc are enveloped with a swirling jet of water. The injection of water serves to constrict the plasma jet and thus increase its cutting ability. The water is also helpful in cooling the nozzle assembly and thus increasing the life of the assembly.
While the benefits of the water injection system are recognized, it has been found that the injection of a sufficient amount of water to properly cool the nozzle assembly has the adverse effect of also cooling the plasma jet and thus reducing its cutting effectiveness. Thus, in existing torches, the dual objectives of achieving maximum cooling of the nozzle assembly, and proper restriction of the plasma jet without unduly cooling the jet, have not been realized.
It is accordingly an object of the present invention to provide a plasma arc torch having an improved nozzle assembly which effectively provides maximum cooling of the nozzle assembly and proper constriction of the arc without unduly cooling the arc.